Polyglycerol esters, per se, are well known in the art. They have various uses, such as components of cleansing, bath, and shampoo compositions, and as cosmetics and food additives.
Conventionally polyglycerol esters are manufactured in a batch process starting with a two-phase reaction mixture: a polyglycerol phase (hydrophilic) and a fatty acid phase (lipophilic). When the mixture is heated, the esterification reaction occurs at the interface of the two phases, initially yielding a highly substituted polyglycerol ester. High temperatures and extended mixing periods are necessary to effect the redistribution of the ester groups from the highly substituted ester to the unreacted polyglycerol, commonly referred to as transesterification. It is only when the transesterification is completed that the reaction mixture becomes the desired clear, single-phase solution.
Other examples of known processes for producing polyol fatty acid esters are:
(1) U.S. Pat. Nos. 3,963,699 and 4,517,360 assigned to The Procter & Gamble Company. Both relate to a transesterification process where a homogeneous reaction melt of a polyol, a fatty acid lower alkyl ester, an alkali metal fatty acid soap, and a basic catalyst is first formed. Additional fatty acid lower alkyl esters are added to the product of the initial step to produce polyol fatty acid polyesters. Such processes use fatty acid lower alkyl esters (rather than fatty acids) and transesterification rather than direct esterification. PA1 (2) U.S. Pat. Nos. 5,006,648, 5,071,975, and 5,079,355 assigned to Van den Bergh Foods Co. The first two patents teach processes for preparing highly substituted polyol fatty acid esters (and lower substituted esters) by mixing a polyol with an alkaline catalyst to prepare a first reactant mixture, mixing a fatty acid lower alkyl ester with a fatty soap to prepare a second reactant mixture, and thereafter blending the two mixtures. The reaction is conducted at the relatively low temperature of 100.degree.-180.degree. C. due to the relatively high soap levels used. PA1 U.S. Pat. No. 5,079,355 discloses a transesterification process wherein a mixture of polyol, fatty acid lower alkyl ester, transesterification catalyst, and alkali metal soap is reacted under transesterification conditions,